Drill rigs are normally used to drill vertical wells. Slant drill rigs, however, may drill wells at angles inclined to the vertical. Thus, a plurality of wells may be drilled from a single location which is environmentally and economically attractive. Service rigs are used to remove and replace pipe tubing and sucker rods in production wells for cleaning or repair subsequent to drilling. Such service rigs must operate at the same angle at which the well was drilled.
In drilling or servicing slant wells, the guide path of the travelling block of the rig must be aligned with the centre lineC of the well hole. This is so because removing well tubing out of alignment with the well centre line can damage the tubing and create a moment resulting in undesirable forces. In previous slant rigs, the hoisting apparatus was approximately aligned with the well centre line by adjusting the rig relative to the carrier. Such adjusting mechanisms, however, are expensive, heavy and complicated.
Yet a further problem in using existing slant rigs lies in the use of such rigs with vertically drilled wells. Previous slant rigs could not service both vertical and slant drilled wells without utilizing a telescoping type mast arrangement which gave rise to structural integrity and stability problems.